Supplemental hot water heat for forced air furnaces

ABSTRACT

A hot water heat exchanger system for a forced air furnace includes a radiator having a water inlet and a water outlet. A first water conduit is mounted in fluid communication between the water inlet and a hot water outfeed line of a hot water tank. A water pump is mounted on the first water conduit for urging hot water from the tank into the radiator. A second water conduit is mounted in fluid communication between the water outlet and a cold water infeed line into the tank. The radiator is mounted into a plenum of the furnace so that air forced from the furnace into outflow ducting of the furnace by operation of a furnace fan in the furnace flows through the radiator, wherein the fan is actuated by a temperature sensor in the furnace. The pump is thermostatically controlled by a first thermostatic sensor. A furnace heater of the furnace is thermostatically controlled by a second thermostatic sensor. The first thermostatic sensor is for actuating the pump in a first temperature range between a desired temperature and a lower threshold temperature. The second thermostatic sensor is for actuating the furnace heater in a second temperature range, wherein the second temperature range is a range of temperatures below the first temperature range.

FIELD OF THE INVENTION

[0001] This invention relates to a supplemental heating system wherein a hot water heat exchanger installed within the plenum of a forced air furnace, is used to maintain the ambient air temperature of a dwelling above a predetermined lower limit.

BACKGROUND OF THE INVENTION

[0002] It is common to heat a residence by distributing air warmed by a furnace to each habitable room, through distribution ducts emanating from a hot air plenum of the furnace. More effective warm air distribution occurs when the furnace has a fan which forces the air through the distribution ducts. Operation of the burner of the furnace and the fan is usually controlled by way of a thermostat located within a room of the dwelling. It is also common to supply a constant source of hot water for use by the residents of the dwelling from a hot water tank. In most residences there is no direct connection between the hot air heating system and the hot water system.

[0003] The prior art as described below discloses the use of water supplied from a domestic water heater circulated through a heat exchanger located within the plenum of a forced air furnace. However, the sensitivity of most thermostats results in a temperature variance of up to several degrees between actuation and shut-off centered about the temperature setting selected on the thermostat by the user. Since the most common thermostats contain a temperature-sensing element either in the form of a bimetal rod or a mercury tilt switch, these are prone, over time, to hysterises which can result in larger than comfortable differentials or swings in room temperature.

[0004] Through the incorporation of a secondary heating source, that is, a water-to-air heat exchanger within the furnace plenum, actuated by a heat sensing-element independent from that of the element operating a primary heating source, that is, the furnace, differentials or swings in room temperature may be dampened to provide a more constant room temperature..

[0005] By setting the heat-sensing element for the secondary heating source to trigger at a higher, or at least slightly higher temperature than the heat-sensing element for the primary heating source, the temperature of the room will remain above that which would normally activate the primary heating source for an extended length of time. This may result in a cost saving to the user since the amount of fuel required to maintain the preset temperature of water within a domestic hot water tank may be significantly less than that required to operate the furnace.

[0006] Further, the independent operation of the secondary heating source during relatively mild but unseasonably cool periods, without operation of the primary heating source, may also result in a significant cost savings to the user.

[0007] In the prior art applicant is aware of U.S. Pat. No. 4,134,448, to Luksus, which discloses the use of a conventional domestic hot water heater to supply heated water to a heat exchanger positioned within the plenum of a forced air furnace. Luksus does not however suggest that, during normal winter conditions, minor fluctuations in ambient room temperature resulting from thermostatic operating sensitivity may be dampened or ameliorated by coordinating the operation of the hot water heat exchanger and forced air fan of the furnace when after the ambient room temperature is above that which results in the furnace heating operation.

[0008] Further, in the prior art applicant is also aware of U.S. Pat. No. 4,371,111, to Pernosky, which also discloses the use of a hot water heater to supply hot water to a heat exchanger placed within the plenum of a forced air distribution system.

SUMMARY OF THE INVENTION

[0009] The present invention incorporates a supplemental hot water heating source within a conventional forced air furnace having a fan. A supplemental water-to-air heat exchanger in the form, by way of example, of a conventional radiator, is secured, for example mounted, within the plenum of the furnace. Return air ducting, integral with the furnace, conveys air from the dwelling to the return air side of the furnace. Distribution ducting conveys heated air from the plenum of the furnace to the rooms within the dwelling by operation of the furnace fan and temperature sensitive controls located within a room of the dwelling. The temperature sensitive controls, alternatively referred to herein as thermostats, independently control the operation of the furnace and the supply of water from the hot water tank to the water-to-air heat exchanger.

[0010] The supplemental water-to-air heat exchanger radiator is connected to the domestic hot water tank through suitable supply line piping extending from the hot water outlet side of the hot water tank to the inlet side of the water-to-air heat exchanger and return line piping extending from the outlet side of the heat exchanger to the cold water inlet side of the hot water tank. An electrical water pump installed in the water supply line piping extending from the hot water tank to the furnace ensures circulation of water through the water-to-air heat exchanger. The hot water tank generally contains a temperature sensitive control, which maintains the water at a preset temperature.

[0011] A thermostat installed in a room of the dwelling controls the operation of the water pump to circulate hot water from the tank to the water-to-air heat exchanger. A heat sensitive limiting switch positioned within the furnace plenum, in proximity to the water-to-air heat exchanger, operates the fan within the furnace to force air through the heat exchanger into the rooms of the dwelling.

[0012] It is therefore one object of the present invention to provide a supplemental hot water heating system operating in cooperation with a forced air furnace, where a water-to-air heat exchanger in the form of a radiator is incorporated within the plenum of the furnace, and the water-to-air heat exchanger is suitably connected to a supply of water from a hot water tank. It is a further object to provide thermostatic control for the circulation of water through the water-to air heat exchanger and operation of the furnace fan distinct from the normal thermostatic control operation of the furnace, thus allowing the supplemental hot water heating system to be utilized as the sole heating source for the dwelling or building. It is yet a further object of the present invention to provide a supplemental hot water heating system operating in cooperation with the forced air furnace where the supplemental heating system is thermostatically controlled so as to operate within a temperature range generally matching the sensitivity range of the forced air heating system thermostat, thereby substantially eliminating differentials or swings in room temperature during winter weather.

[0013] In summary, the hot water heat exchanger system of the present invention for a forced air furnace includes a radiator having a water inlet and a water outlet. A first water conduit is mounted or mountable in fluid communication between the water inlet and a hot water outfeed line of a hot water tank. A water pump is mounted or mountable on the first water conduit for urging hot water from the tank into the radiator. A second water conduit is mounted or mountable in fluid communication between the water outlet and a cold water infeed line into the tank.

[0014] The radiator is mounted or mountable into a plenum of the furnace so that air forced from the furnace into outflow ducting of the furnace by operation of a furnace fan in the furnace flows through the radiator, wherein the fan is actuated by a temperature sensor in the furnace. The pump is thermostatically controlled by a first thermostatic sensor. A furnace heater of the furnace is thermostatically controlled by a second thermostatic sensor.

[0015] The first thermostatic sensor is for actuating the pump in a first temperature range between a desired temperature and a lower threshold temperature. The second thermostatic sensor is for actuating the furnace heater in a second temperature range, wherein the second temperature range is a range of temperatures below the first temperature range. As a result, as a sensed temperature sensed by the first and second thermostatic sensors drops below the desired temperature into the first temperature range, the pump is actuated so as to heat air in the plenum by hot water circulation through the radiator thereby actuating the fan to force air warmed by the radiator into the outflow ducting. When the radiator cannot maintain the sensed temperature in the first temperature range so that the temperature sensed by the first and second sensors drops below the lower threshold temperature and into the second temperature range, the furnace heater is actuated to assist in elevating the sensed temperature to the desired temperature.

[0016] In one embodiment, the desired temperature may be adjusted by a user adjusting a thermostatic control setting of a thermostatic controller of the first thermostatic sensor, and the lower threshold temperature may be adjusted by the user adjusting a thermostatic control setting of a thermostatic controller of the second thermostatic sensor. In one embodiment the first and second thermostatic sensors may be mounted or are mountable in a single thermostat housing. The first and second thermostatic sensors may be mercury switches.

[0017] In one embodiment an air reservoir, for dampening pressure fluctuations in the first water conduit, is mounted or mountable in fluid communication on the first water conduit.

[0018] In the present invention, the method of hot water heating of air flowing through the furnace includes the steps of:

[0019] (a) adjusting the first thermostatic sensor for actuating the pump in the first temperature range between a desired temperature and the lower threshold temperature, and

[0020] (b) adjusting the second thermostatic sensor for actuating the furnace heater in the second temperature range, again, wherein the second temperature range is below the first temperature range.

BRIEF DESCRIPTION OF THE DRAWINGS

[0021]FIG. 1 is a schematic perspective view of the heating system of the present invention.

[0022]FIG. 2 is a schematic electrical diagram of the heating system of the present invention.

[0023]FIG. 3 is a front elevational view of a dual-acting thermostat containing mercury tilt switches.

DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION

[0024] With reference to the drawing figures wherein similar characters of reference denote corresponding parts in each view, the supplemental hot water heating apparatus of the present invention 10, incorporates a water-to-air heat exchanger or radiator 12 positioned within the plenum 14 of a conventional forced air furnace 16. A squirrel-cage fan 18 operating within furnace 16 draws air in direction A from the dwelling or building to the furnace through return ducting 20, through an air-to-air heat exchanger 22 and through water-to-air heat exchanger 12, forcing the air back into the dwelling in direction B through distributing ducting 26.

[0025] A supply water line 32 for the water-to-air heat exchanger 12 is connected to the hot water outlet line 24 from a conventional hot water tank 30. Hot water flows in direction C from tank 30 to heat exchanger 12. Supply line 32 may have a shut off valve 32 a; expansion tank 34 and electric water pump 36. A temperature sensitive switch 38 is positioned and mounted within the furnace plenum and is electrically connected to fan 18. The electrical connection is shown in dotted outline. Triggering switch 38 operates fan 18. Switch 38 is positioned within the furnace plenum 14 such that a rise in temperature within plenum 14 resulting from either the circulation of water through the water-to-air heat exchanger 12 or furnace operation which increases the temperature within the air-to-air heat exchanger 22 results in operation of fan 18 to force air through distributing ducting 26 into the rooms of a dwelling.

[0026] The water return line 42 from water-to-air heat exchanger 12 is connected to the incoming cold water supply line 44 for tank 30 through a check valve 46. Cooled water from heat exchanger 12 flows in direction D to a T-junction with supply line 44. Other isolation valves labelled ‘V’, as are appropriate for such a system and would be known to those skilled in the art are also illustrated.

[0027] As may be seen illustrated schematically in the electrical diagram in FIG. 2, electric water pump 36 and squirrel-cage fan 18 are connected through temperature-sensitive switch 38. Thermostat 50 may be a two-stage thermostat as manufactured by White Rodgers Division, Emerson Electric, which upon a room temperature differential, may operate either the pump 36 or the furnace gas valve 52 thereby heating plenum 14 of furnace 16. Upon reaching a predetermined temperature, switch 38 powers fan 18 to distribute warm air throughout the dwelling.

[0028] As may be seen in FIG. 3, thermostat 50 has two mercury tilt switches 54 and 56. Upper tilt switch 54 operates the secondary heating source and lower tilt switch 56 operates the primary heating source. Switch 54 operates within a temperature sensitivity range slightly above the temperature sensitivity range of switch 56. When switch 54 is closed, pump 36 circulates water from tank 30 through the air-to-air heat exchanger 22. A rise in air temperature within the plenum 14 of furnace 16 results in the closing of temperature switch 38 and the actuation of furnace fan 18 to circulate warm air throughout the dwelling.

[0029] Should the circulating warm air through the water-to-air heat exchanger 22 be insufficient to maintain the room temperature above that of the sensitivity range of lower tilt switch 56, it will close to actuate gas valve 52 to increase the air temperature delivered to the dwelling.

[0030] As will be apparent to those skilled in the art in the light of the foregoing disclosure, many alterations and modifications are possible in the practice of this invention without departing from the spirit or scope thereof. Accordingly, the scope of the invention is to be construed in accordance with the substance defined by the following claims. 

What is claimed is:
 1. A hot water heat exchanger system for a forced air furnace comprising: a radiator having a water inlet and a water outlet, a first water conduit mountable in fluid communication between said water inlet and a hot water outfeed line of a hot water tank, a water pump mountable on said first water conduit for urging hot water from said tank into said radiator, a second water conduit mountable in fluid communication between said water outlet and a cold water infeed line into said tank, said radiator mountable into a plenum of said furnace so that air forced from said furnace into outflow ducting of said furnace by operation of a furnace fan flows through said radiator, said fan actuated by a temperature sensor in said furnace, said pump thermostatically controlled by a first thermostatic sensor, a furnace heater thermostatically controlled by a second thermostatic sensor, said first thermostatic sensor for actuating said pump in a first temperature range between a desired temperature and a lower threshold temperature, said second thermostatic sensor for actuating said furnace heater in a second temperature range wherein said second temperature range is below said first temperature range, whereby, as a sensed temperature sensed by said first and second thermostatic sensors drops below said desired temperature into said first temperature range, said pump is actuated so as to heat air in said plenum by hot water circulation through said radiator thereby actuating said fan to force air warmed by said radiator into said outflow ducting, and whereby, if said radiator cannot maintain the sensed temperature in the first temperature range so that the temperature sensed by said first and second sensors drops below said lower threshold temperature and into said second temperature range, said furnace heater is actuated to assist in elevating the sensed temperature to the desired temperature.
 2. The device of claim 1 wherein an air reservoir, for dampening pressure fluctuations in said first water conduit, is mountable in fluid communication on said first water conduit.
 3. The device of claim 1 wherein said first and second thermostatic sensors are mountable in a single thermostat housing.
 4. The device of claim 3 wherein said first and second thermostatic sensors are mercury switches.
 5. In a hot water heat exchanger system for a forced air furnace including: a radiator having a water inlet and a water outlet, a first water conduit mounted in fluid communication between the water inlet and a hot water outfeed line of a hot water tank, a water pump mounted on the first water conduit for urging hot water from the tank into the radiator, a second water conduit mounted in fluid communication between the water outlet and a cold water infeed line into the tank, the radiator mounted into a plenum of the furnace so that air forced from the furnace into outflow ducting of the furnace by operation of a furnace fan flows through the radiator, the fan actuated by a temperature sensor in the furnace, the pump thermostatically controlled by a first thermostatic sensor, a furnace heater thermostatically controlled by a second thermostatic sensor, a method of hot water heating of air flowing through the furnace comprising the steps of: (a) adjusting said first thermostatic sensor for actuating said pump in a first temperature range between a desired temperature and a lower threshold temperature, and (b) adjusting said second thermostatic sensor for actuating said furnace heater in a second temperature range wherein said second temperature range is below said first temperature range, whereby, as a sensed temperature sensed by said first and second thermostatic sensors drops below said desired temperature into said first temperature range, said pump is actuated so as to heat air in said plenum by hot water circulation through said radiator thereby actuating said fan to force air warmed by said radiator into said outflow ducting, and whereby, if said radiator cannot maintain the sensed temperature in the first temperature range so that the temperature sensed by said first and second sensors drops below said lower threshold temperature and into said second temperature range, said furnace heater is actuated to assist in elevating the sensed temperature to the desired temperature.
 6. The method of claim 5 comprising the further step of mounting an air reservoir, for dampening pressure fluctuations in said first water conduit, in fluid communication with said first water conduit.
 7. The method of claim 5 comprising the further step of mounting said first and second thermostatic sensors in a single thermostat housing.
 8. The device of claim 1 wherein said first and second thermostatic sensors include thermostatic controllers cooperating therewith, said controllers selectively adjustable so as to allow adjustable setting of said desired temperature and said lower threshold temperature.
 9. A hot water heat exchanger system for a forced air furnace comprising: a radiator having a water inlet and a water outlet, a first water conduit is mounted in fluid communication between said water inlet and a hot water outfeed line of a hot water tank, a water pump is mounted on said first water conduit for urging hot water from said tank into said radiator, a second water conduit is mounted in fluid communication between said water outlet and a cold water infeed line into said tank, said radiator is mounted into a plenum of said furnace so that air forced from said furnace into outflow ducting of said furnace by operation of a furnace fan flows through said radiator, said fan actuated by a temperature sensor in said furnace, said pump thermostatically controlled by a first thermostatic sensor, a furnace heater thermostatically controlled by a second thermostatic sensor, said first thermostatic sensor for actuating said pump in a first temperature range between a desired temperature and a lower threshold temperature, said second thermostatic sensor for actuating said furnace heater in a second temperature range wherein said second temperature range is below said first temperature range, whereby, as a sensed temperature sensed by said first and second thermostatic sensors drops below said desired temperature into said first temperature range, said pump is actuated so as to heat air in said plenum by hot water circulation through said radiator thereby actuating said fan to force air warmed by said radiator into said outflow ducting, and whereby, if said radiator cannot maintain the sensed temperature in the first temperature range so that the temperature sensed by said first and second sensors drops below said lower threshold temperature and into said second temperature range, said furnace heater is actuated to assist in elevating the sensed temperature to the desired temperature.
 10. The device of claim 9 wherein an air reservoir, for dampening pressure fluctuations in said first water conduit, is mountable in fluid communication on said first water conduit.
 11. The device of claim 9 wherein said first and second thermostatic sensors are mountable in a single thermostat housing.
 12. The device of claim 9 wherein said first and second thermostatic sensors are mercury switches.
 13. The device of claim 9 wherein said first and second thermostatic sensors include thermostatic controllers cooperating therewith, said controllers selectively adjustable so as to allow adjustable setting of said desired temperature and said lower threshold temperature. 